The invention pertains generally to a subscriber terminal for CATV or other subscription television systems and is more particularly directed to a method and an apparatus for reprogramming a subscriber terminal.
The subscriber terminal, more commonly known as a set top terminal, is an integral component of subscription television systems. These subscription television systems can be cable television (CATV) systems, SMATV systems, multi-point, multi-distribution (MMDS) systems, or direct-to-home (DTH) systems. The terminals have conventionally provided the functions of tuning particular channels of the subscription television system which are outside the subscriber""s television receiver capability. Further, they provide conditional access to the particular subscription service through authorization codes and in many services provide tiering or authorization of particular channels of the service by descrambling.
More recently, the subscriber terminal has become user friendly by providing an interactive, on-screen display and other user functions that allow the subscriber to manipulate the subscription service and his television receiver in additional ways. These features include such things as volume control, pay-per-view event confirmation, favorite channel listings, sleep timer features, parental control capability, messaging, program timers for recording VCR programs, and other consumer friendly operational features.
In addition, some of the features found in newer television receivers can be provided for older receivers by the subscription terminal. For example, channel identifiers, mute and volume control can be accomplished by the subscriber terminal making the subscriber""s television receiver appear to be a newer model with these capabilities.
An advantageous example of a subscriber terminal with these advanced consumer features is the 8600 model series of subscriber terminals manufactured by Scientific-Atlanta, Inc. of Lawrenceville, Ga.
Currently, these subscriber terminals are controlled by programmable microcontrollers which have their control programs stored in a read only memory (either integral with the microprocessor or included in a separate integrated circuit) or stored in a separate non-volatile memory such as an EPROM or a battery backed up RAM. With the current programming methods, the control program of the subscriber terminal can only be changed by removing the memory device (or the device incorporating the memory) and replacing it. This method is very inconvenient and expensive for changes which are to be made to subscriber terminals as it means a home visit from the service personnel of the subscription service provider. Subscription television systems may have several hundred thousand subscriber terminals which may need such upgrades.
Therefore, it would be advantageous to be able to reprogram the subscriber terminals of a subscription television service to change on screen parameters, change subscriber interfaces, add new features, and modify the control program from a remote location.
The invention provides a method and an apparatus for allowing a subscriber terminal of a subscription television system to be reprogrammed.
The preferred implementation of the subscriber terminal includes a control microprocessor which includes at least a read only memory (ROM) and random access memory (RAM) which is internal to the microprocessor chip. The memory capability of the microprocessor additionally includes several pages of Flash EPROM memory in 64 k blocks which can be mounted internally to the subscriber terminal or externally in the form of plug-in modules. The memory space may include other types of memory which can be reprogrammed.
The subscriber terminal further has a multifunction control circuit (MCC) which controls the input of data to the subscriber terminal from the headend of the subscription television system. The MCC controls a plurality of decoders for in-band video data, in-band audio data, and out-of-band data which it buffers in a volatile memory area. The data which the subscriber terminal receives occurs in defined transactions between the headend and the subscriber terminal. Among the multiplicity of transactions between the headend and subscriber terminal are several to download program code parameters and another to download program code from the headend into the memory space of the control microprocessor. This capability provides a means to change the control program of the control microprocessor to either upgrade it, add additional features, disable obsolete features, or to correct the performance of certain routines of the control program.
In the preferred embodiment, the ROM of the control microprocessor is but a small part of the overall memory space of the processor and contains a loader program and, optionally, several kernel routines. This system code; collectively termed the boot program, is the only part of the memory space which is static and cannot be reprogrammed. In an alternative embodiment, the boot program further contains a revision number so that the control microprocessor may be upgraded by replacement and matched with reprogrammed control program code if so desired. The subscriber terminal is adapted to receive a download program code parameters transaction from the headend which describes the new control code which is to be downloaded into the memory space of the subscriber terminal. The boot program then utilizes these parameters to receive a plurality of download program code transactions which contain the program code to be stored.
In the illustrated implementation, the download program code parameters transaction indicates the expected number of download program code transactions that are to be received by the subscriber terminal, the channel of the subscription system (in-band or out-of-band) where the information is to be found, and the memory space into which it should be stored.
The boot program receives a plurality of the download program code transactions, possibly multiple times. Once a download program code transaction is accurately received, the program code will be stored in the memory space reserved for it and the count of expected transactions decremented. When all the transactions for a particular reprogramming operation have been received, the expected transaction count will be zero and thereby indicate that the downloading operation is complete. In this manner, the downloading operation may be accomplished efficiently even if one or several transactions are not received the first time they are transmitted.
In accordance with another aspect of the invention, the download parameters transactions can be individually addressed, group addressed or globally addressed while the actual download program code transactions are globally transmitted. This operation permits a small set of transactions, the program code parameters transactions, to direct the storage of a much larger set of transactions, the program code transaction. This dramatically decreases the time it takes to encode and decode addressed transactions in the system. This provides for further efficiencies in reprogramming only certain subscriber terminals or groups of subscriber terminals.
Moreover, the program code parameters transactions may contain a program code revision identifier in order to provide other selective criteria on which to determine which subscriber terminals are reprogrammed. In this manner, a current program code version may be periodically transmitted from the headend to update all terminals for system revisions and to initially program new terminals as they are added to the subscriber base. The system operator is then assured that the entire subscriber base is operating with the same program and that revising a terminal""s software and initially loading the software do not have to be accomplished by different methods.
According to another aspect of the invention, the program code parameters transactions define the memory space destination to which the new program code is to be downloaded. Conveniently, the memory space may be divided into contiguous areas such as a 64 k bytes, which physically may be separate integrated circuits. This permits selected memory chips to be downloaded rather than the entire memory space. This aspect is advantageous when particular types of memory chips are used such as Flash EPROM memory which must be entirely erased before being rewritten. With this method, only those memory chips which need to be changed are erased.
The memory space definition may also include a designation concerning whether the program code which is to be downloaded is to be stored in an internal memory, an external memory, or both. The preferred subscriber terminal has an expandable memory space which can. be augmented with plug-in modules. By being able to direct the downloaded code to either the internal or external memory, a choice can be made of where to store certain basic control routines as opposed to supplemental features. For example, a core of control routines which provide a basic features set of the subscriber terminal can be stored internally. Other features which are special, or are individually or group directed, can be stored externally. This produces an advantageous subscription television system where all the subscriber terminals have a certain common capability based on a common control program loaded into the internal memory space. If the subscriber or subscriber group does not desire or need any of a special or additional features set, the plug-in modules need not be present and their cost saved.